The present invention generally relates to a sintered alloy having an improved wear resistance property for use as a material of a sliding member in an internal combustion engine, and particularly relates to a sintered alloy having an improved wear resistance property for use as a material of a journal member of a cam shaft.
Recently, various members to be used in an internal combustion engine have been required to be capable of enduring against a high load operation, and particularly sliding members such as a cam shaft, a rocker arm, etc., have been required to have durability against a high surface pressure. In order to satisfy this requirement and to reduce the working and material costs of the sliding members and the weight of the same, a sintered material of alloy powder has been examined to be used as the material of the sliding members.
In the case where molybdenum, chromium, or the like, is added into an Fe-C-P alloy system conventionally used as a material of a journal member, a hard carbide principally containing (Fe, Cr).sub.3 C, (Fe, Cr, Mo).sub.3 C, or the like, is formed. Although the matrix of the material is strengthened, martensite transformation or bainite transformation of the base is simultaneously promoted. Therefore, although being superior in wear resistance property, the resultant sintered material is reduced in machinability so that it is unsuitable as the material for the journal member because the material is necessary to be subject to cutting.
Further, in the journal member material such as an Fe-C-P alloy system or an Fe-C-P-Cu alloy system, it is impossible to rapidly complete diffusion among particles when the journal member is sintered in a liquid phase at a high temperature, so that a wrinkle or a crack is generated in the vicinity of the surface of the journal member. In order to cope with the foregoing disadvantage, there has been proposed such a method that chromium or molybdenum is added to the foregoing system. However, the addition has such a problem as described above. Further, it is considered to increase the content of phosphorus. However, if the quantity of phosphorus is increased so much, the liquid phase may become so excessive that a carbide (containing a steadite) is greatly formed.